The overall objectives of the proposed research are to understand the role of population structure in the evolution of species over time, with special reference to interdemic processes such as extinction, recolonization, and dispersion. The specific empirical aims are to: (1) measure the amount of non-additive genetic variance in fitness components in recently collected strains of the flour beetles, Tribolium castaneum and T. confusum; (2) determine the relationship between this non-additive variance and the rate of differentiation of subdivided populations; (3) estimate the genetic variance and covariance between an individual's reproductive performance in a group of constant genotypic composition and the effect of that individual on the reproductive performance of others; (4) determine the response to interdemic selection by differential dispersion-an empirical model of Wright's shifting balance theory. These proposed experiments represent a continuation and extension of research begun under previous awards of this grant. The first three experimental studies are intended to determine whether or not the non-additive genetic variance in components of fitness is a sufficient explanation for the rate and the extent of population differentiation observed in a series of earlier studies conducted under this grant. The fourth experiment represenys an attempt to empirically model interdemic selection by differential dispersion as opposed to differential extinction or recolonization. This mode of interdemic selection has not been previously studied empirically although it is one of the major evolutionary forces in the shifting balance theory. The theoretical aims of the proposed research are to combine drift and selection in two-locus models of subdivided populations. We have had initial success in using the covariance approach of Price to describe the effects of selection in subdivided poulations and with the two-locus coancestry measures to describe random genetic draft in subdivided populations with epistatic gene action.